Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (63,660)	$ (49,851)	$ (46,971)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	480	430	494
Amortization of intangible assets	666	665	666
Stock-based compensation	14,601	10,075	11,287
Net premium amortization and discount on available-for-sale securities	13	5	(521)
Loss on disposal of fixed assets		119
Gain on U.S. Treasury securities		(8)
Changes in operating assets and liabilities:
Accounts receivable	(61)
Inventory	(5,824)
Prepaid expenses and other current assets	(1,374)	194	(226)
Other receivables	54
Right-of-use assets	653	509	68
Other long-term assets		129	(393)
Accounts payable	1,160	(266)	646
Accrued expenses	(937)	2,830	841
Deferred revenue	16
Lease liabilities	(542)	(196)	(76)
Accrued interest on note payable	658
Net cash used in operating activities	(54,097)	(35,365)	(34,185)
Cash flows from investing activities:
Purchases of property and equipment	(437)	(441)	(608)
Purchases of investments		(29,025)	(77,993)
Maturities of investments	8,000	35,000	68,500
Sales of investments		4,510
Net cash provided by (used in) investing activities	7,563	10,044	(10,101)
Cash flows from financing activities:
Proceeds from issuance of common stock under employee stock purchase plan	810	490	423
Proceeds from exercises of warrants	4,217	244
Proceeds from exercises of stock options	786	717	272
Proceeds from issuance of common stock	56,697	29,434
Proceeds from insurance loan agreement	1,939
Payments made on insurance loan agreement	(1,532)
Tax payments related to shares withheld for vested restricted stock units	(232)		(613)
Net cash provided by financing activities	62,685	30,885	82
Net increase (decrease) in cash and cash equivalents	16,151	5,564	(44,204)
Cash and cash equivalents at beginning of period	12,463	6,899	51,103
Cash and cash equivalents at end of period	28,614	12,463	6,899
Supplemental disclosure of noncash investing and financing activities:
Other receivable from exercise of warrants and stock options		1,053
Change in unrealized gains on available-for-sale securities	1	(5)	5
Equipment purchases included in accounts payable and accrued expenses	27	$ 20	$ 279
Accrued interest settled via issuance of common stock from private placement equity offering	$ 629